SVP aidez moi merci !!!!!!!!!!

A=-5/4+3+5/6+5/7-2
A=-105/84+252/84+70/84+60/84-168/84=(-105+252+70+60-168)/84
A=109/84

B=-28/27*(-72)/(-35)=-(4*7)/(3*9)*(3*24)/(5*7)
B=-4/9*24/5=-96/45=-32/15